NSLS X1B - AN UNDULATOR BEAMLINE FOR HIGH-RESOLUTION SOFT-X-RAY SPECTROSCOPY

The X1 undulator on the X-ray ring of the NSLS at Brookhaven is an extremely bright source of soft X-ray photons. On the recently completed spectroscopy beamline X1B we have attempted to utilise the intrinsically narrow beam size and divergence to maximise the intensity throughput in a spherical grating monochromator (SGM). The high power density of the undulator radiation requires the use of water cooled mirrors, entrance slit and grating. Calculations predict that simple side cooled copper pads attached to optical elements will be sufficiently effective that resolution degradation due to thermal deformation of figure error will be negligible in the SGM design. This is confirmed by attainment of resolution superior to other SGMs and the BESSY SX700-II monochromator over the energy range 300-540 eV (C1s-1, N1s-1 and O1s-1). At a resolution comparable to the best so far obtained for the nitrogen N1s-pi* excitation (401 eV) on other monochromators we have demonstrated an intensity increase, at the sample, of more than three orders of magnitude. The design considerations upon which beamline X1B is based are highly relevant to thc construction of soft X-ray monochromators at future synchrotron radiation sources such as the ALS (Berkeley), Elettra (Trieste) and BESSYII (Berlin).